BIP 0061

From Bitcoin.com Wiki
Jump to: navigation, search
  BIP: 61
  Title: Reject P2P message
  Author: Gavin Andresen <gavinandresen@gmail.com>
  Status: Final
  Type: Standards Track
  Created: 2014-06-18

Abstract

This BIP describes a new message type for the Bitcoin peer-to-peer network.

Motivation

Giving peers feedback about why their blocks or transactions are rejected, or why they are being banned for not following the protocol helps interoperability between different implementations.

It also gives SPV (simplified payment verification) clients a hint that something may be wrong when their transactions are rejected due to insufficient priority or fees.

Specification

Data types in this specification are as described at https://en.bitcoin.it/wiki/Protocol_specification

reject

One new message type "reject" is introduced. It is sent directly to a peer in response to a "version", "tx" or "block" message.

For example, the message flow between two peers for a relayed transaction that is rejected for some reason would be:

--> inv
<-- getdata
--> tx
<-- reject

All implementations of the P2P protocol version 70,002 and later should support the reject message.

common payload

Every reject message begins with the following fields. Some messages append extra, message-specific data.

Field Size Name Data type Comments
variable response-to-msg var_str Message that triggered the reject
1 reject-code uint8_t 0x01 through 0x4f (see below)
variable reason var_string Human-readable message for debugging

The human-readable string is intended only for debugging purposes; in particular, different implementations may use different strings. The string should not be shown to users or used for anthing besides diagnosing interoperability problems.

The following reject code categories are used; in the descriptions below, "server" is the peer generating the reject message, "client" is the peer that will receive the message.

Range Category
0x01-0x0f Protocol syntax errors
0x10-0x1f Protocol semantic errors
0x40-0x4f Server policy rule

rejection codes common to all message types

Code Description
0x01 Message could not be decoded

reject version codes

Codes generated during the intial connection process in response to a "version" message:

Code Description
0x11 Client is an obsolete, unsupported version
0x12 Duplicate version message received

reject tx payload, codes

Transaction rejection messages extend the basic message with the transaction id hash:

Field Size Name Data type Comments
32 hash char[32] transaction that is rejected

The following codes are used:

Code Description
0x10 Transaction is invalid for some reason (invalid signature, output value greater than input, etc.)
0x12 An input is already spent
0x40 Not mined/relayed because it is "non-standard" (type or version unknown by the server)
0x41 One or more output amounts are below the 'dust' threshold
0x42 Transaction does not have enough fee/priority to be relayed or mined

payload, reject block

Block rejection messages extend the basic message with the block header hash:

Field Size Name Data type Comments
32 hash char[32] block (hash of block header) that is rejected

Rejection codes:

code description
0x10 Block is invalid for some reason (invalid proof-of-work, invalid signature, etc)
0x11 Block's version is no longer supported
0x43 Inconsistent with a compiled-in checkpoint

Note: blocks that are not part of the server's idea of the current best chain, but are otherwise valid, should not trigger reject messages.

Compatibility

The reject message is backwards-compatible; older peers that do not recognize the reject message will ignore it.

Implementation notes

Implementors must consider what happens if an attacker either sends them reject messages for valid transactions/blocks or sends them random reject messages, and should beware of possible denial-of-service attacks. For example, notifying the user of every reject message received would make it trivial for an attacker to mount an annoy-the-user attack. Even merely writing every reject message to a debugging log could make an implementation vulnerable to a fill-up-the-users-disk attack.